Magnetic detector and method for producing the same

ABSTRACT

A magnetic detector includes a full-bridge circuit including magnetoresistive sensors on the same substrate. The magnetoresistive sensors include two magnetoresistive films and have different relationships between the fixed magnetization direction and the bias application direction. The fixed magnetization direction and the bias application direction are determined with three or more exchange coupling films including antiferromagnetic layers with different blocking temperatures. Thus, the magnetic detector has high resistance to a strong magnetic field, is easy to produce, and has a high degree of flexibility in production.

CLAIM OF PRIORITY

This application is a Continuation of International Application No.PCT/JP2018/047857 filed on Dec. 26, 2018, which claims benefit ofpriority to Japanese Patent Application No. 2018-005458 filed on Jan.17, 2018. The entire contents of each application noted above are herebyincorporated by reference.

BACKGROUND 1. Field of the Disclosure

The present disclosure relates to a magnetic detector that includes afull-bridge circuit including a plurality of magnetoresistive sensorswith a magnetoresistive film and a method for producing the magneticdetector.

2. Description of the Related Art

Magnetic detectors (magnetic sensors) that include a magnetoresistivesensor with a magnetoresistive film having a pinned magnetic layer and afree magnetic layer are used in various fields, such as magnetic fieldsensors, position sensors, and electric current sensors. To improve thedetection accuracy and broaden the measurable range of such sensors,some magnetic sensors include a full-bridge circuit (Wheatstone bridgecircuit) composed of half-bridge circuits connected in parallel. Thehalf-bridge circuits each include two magnetoresistive sensors withdifferent responsiveness to an external magnetic field connected inseries. The two magnetoresistive sensors in the full-bridge circuittypically have different relative relationships between themagnetization direction and the sensitivity axis direction of the freemagnetic layer in the absence of an external magnetic field andtherefore have different responsiveness to an external magnetic field.

For example, Japanese Unexamined Patent Application Publication No.2006-527497 discloses two magnetoresistive sensors with antiparallelfixed magnetization axes. PCT Japanese Translation Patent PublicationNo. 2014-516406 discloses two magnetoresistive sensors that have fixedmagnetization axes in the same direction and include free magneticlayers to which a bias magnetic field is applied in differentdirections.

In Japanese Unexamined Patent Application Publication No. 2006-527497,in order to differentiate the directions of the fixed magnetization axesof a plurality of magnetoresistive sensors on a substrate, at least oneof the magnetoresistive sensors is selectively heated by applying anelectric current in a magnetic field to heat an antiferromagnetic layerof the magnetoresistive sensor(s) to its blocking temperature or higherand adjust the magnetization direction of the antiferromagnetic layer tothe magnetization direction of the pinned magnetic layer parallel to theexternal magnetic field application direction, thereby setting the fixedmagnetization axis of the heated magnetoresistive sensor in the desireddirection.

In PCT Japanese Translation Patent Publication No. 2014-516406, the twomagnetoresistive sensors with the fixed magnetization axes in the samedirection are formed on the same substrate, wherein the free magneticlayers in the absence of an external magnetic field have differentdirections. A method for controlling the direction of the free magneticlayer described therein utilizes the shape anisotropy of amagnetoresistive film, utilizes a bias magnetic field of a permanentmagnet, or includes placing an antiferromagnetic layer on the freemagnetic layer to generate an exchange coupling magnetic field, forexample.

SUMMARY

In one aspect of the disclosure, a magnetic detector that includes afull-bridge circuit including a first magnetoresistive sensor and asecond magnetoresistive sensor. The first magnetoresistive sensorincludes a first magnetoresistive film including a first pinned magneticlayer and a first free magnetic layer. The second magnetoresistivesensor includes a second magnetoresistive film including a second pinnedmagnetic layer and a second free magnetic layer. The full-bridge circuitincludes a first half-bridge circuit and a second half-bridge circuitconnected in parallel between a power supply terminal and a groundterminal. The first half-bridge circuit includes the firstmagnetoresistive sensor and the second magnetoresistive sensor connectedin series and the second half-bridge circuit includes the secondmagnetoresistive sensor and the first magnetoresistive sensor connectedin series. The first magnetoresistive sensor and the secondmagnetoresistive sensor are located on the same substrate, in the firstmagnetoresistive film. The first pinned magnetic layer and a firstpinning antiferromagnetic layer located on an opposite side of the firstpinned magnetic layer from the first free magnetic layer constitute afirst pinning exchange coupling film, and the first free magnetic layerand a first biasing antiferromagnetic layer located on an opposite sideof the first free magnetic layer from the first pinned magnetic layerconstitute a first biasing exchange coupling film.

In the second magnetoresistive film, the second pinned magnetic layerand a second pinning antiferromagnetic layer located on an opposite sideof the second pinned magnetic layer from the second free magnetic layerconstitute a second pinning exchange coupling film, and the second freemagnetic layer and a second biasing antiferromagnetic layer located onan opposite side of the second free magnetic layer from the secondpinned magnetic layer constitute a second biasing exchange couplingfilm. The first pinned magnetic layer has a fixed magnetization axiscoaxial with a fixed magnetization axis of the second pinned magneticlayer. The first biasing exchange coupling film has an exchange couplingmagnetic field direction nonparallel to a fixed magnetization axisdirection of the first pinned magnetic layer, and the second biasingexchange coupling film has an exchange coupling magnetic field directionnonparallel to a fixed magnetization axis direction of the second pinnedmagnetic layer. Each of a blocking temperature Tbf1 of the first pinningantiferromagnetic layer and a blocking temperature Tbf2 of the secondpinning antiferromagnetic layer is higher than a blocking temperatureTb1 of the first biasing antiferromagnetic layer and a blockingtemperature Tb2 of the second biasing antiferromagnetic layer, and theblocking temperature Tb1 of the first biasing antiferromagnetic layer ishigher than the blocking temperature Tb2 of the second biasingantiferromagnetic layer.

As described above, at least three antiferromagnetic layers withdifferent blocking temperatures Tbs can be used to flexibly determinethe fixed magnetization axis direction and the bias magnetic fieldapplication direction in the free magnetic layer in two magnetoresistivedevices. Furthermore, both the fixed magnetization axis and the biasmagnetic field are set using an exchange coupling magnetic field betweenan antiferromagnetic layer and a ferromagnetic layer. This increasesresistance to a strong magnetic field. Furthermore, two adjacentmagnetoresistive devices have little influence on each other. Thus, themagnetic detector can be miniaturized compared with the case where thebias magnetic field is set with a permanent magnet, for example.

In another aspect, a method for producing a magnetic detector includinga full-bridge circuit includes a first magnetoresistive sensor and asecond magnetoresistive sensor, the first magnetoresistive sensorincluding a first magnetoresistive film including a first pinnedmagnetic layer and a first free magnetic layer. The secondmagnetoresistive sensor includes a second magnetoresistive filmincluding a second pinned magnetic layer and a second free magneticlayer.

In the magnetic detector produced by the production method, a thefull-bridge circuit includes a first half-bridge circuit and a secondhalf-bridge circuit connected in parallel between a power supplyterminal and a ground terminal. The first half-bridge circuit includesthe first magnetoresistive sensor and the second magnetoresistive sensorconnected in series and the second half-bridge circuit includes thesecond magnetoresistive sensor and the first magnetoresistive sensorconnected in series. The first magnetoresistive sensor and the secondmagnetoresistive sensor are located on the same substrate, in the firstmagnetoresistive film. The first pinned magnetic layer and a firstpinning antiferromagnetic layer located on an opposite side of the firstpinned magnetic layer from the first free magnetic layer constitute afirst pinning exchange coupling film, and the first free magnetic layerand a first biasing antiferromagnetic layer located on an opposite sideof the first free magnetic layer from the first pinned magnetic layerconstitute a first biasing exchange coupling film.

In the second magnetoresistive film, the second pinned magnetic layerand a second pinning antiferromagnetic layer located on an opposite sideof the second pinned magnetic layer from the second free magnetic layerconstitute a second pinning exchange coupling film, and the second freemagnetic layer and a second biasing antiferromagnetic layer located onan opposite side of the second free magnetic layer from the secondpinned magnetic layer constitute a second biasing exchange couplingfilm. Each of a blocking temperature Tbf1 of the first pinningantiferromagnetic layer and a blocking temperature Tbf2 of the secondpinning antiferromagnetic layer is higher than a blocking temperatureTb1 of the first biasing antiferromagnetic layer and a blockingtemperature Tb2 of the second biasing antiferromagnetic layer, and theblocking temperature Tb1 of the first biasing antiferromagnetic layer ishigher than the blocking temperature Tb2 of the second biasingantiferromagnetic layer. Such a production method includes a fixedmagnetization axis setting step of ordering the first pinningantiferromagnetic layer and the second pinning antiferromagnetic layerby heat treatment to generate an exchange coupling magnetic field in thefirst biasing exchange coupling film and in the second biasing exchangecoupling film, thereby making a fixed magnetization axis of the firstpinned magnetic layer coaxial with a fixed magnetization axis of thesecond pinned magnetic layer, a first bias magnetic field setting stepof making a direction of a bias magnetic field generated by the firstbiasing exchange coupling film nonparallel to a fixed magnetization axisdirection of the first pinned magnetic layer by heat treatment in anexternal magnetic field at a temperature lower than a blockingtemperature Tbf1 of the first pinning antiferromagnetic layer and ablocking temperature Tbf2 of the second pinning antiferromagnetic layer,and after the first bias magnetic field setting step, a second biasmagnetic field setting step of making a direction of a bias magneticfield generated by the second biasing exchange coupling film nonparallelto a fixed magnetization axis direction of the second pinned magneticlayer by heat treatment in an external magnetic field at a temperaturelower than the blocking temperature Tb1 of the first biasingantiferromagnetic layer.

The production method enables the production of a magnetic detector thatincludes a full-bridge circuit (Wheatstone bridge circuit) including twomagnetoresistive sensors with different responsiveness to an externalmagnetic field on the same substrate and that has high resistance to astrong magnetic field without the step of applying an external magneticfield to each magnetoresistive sensor.

The present invention can provide a magnetic detector that includes afull-bridge circuit including two magnetoresistive sensors withdifferent responsiveness to an external magnetic field on the samesubstrate and that has high resistance to a strong magnetic field. Thepresent invention can also provide a method for producing the magneticdetector.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory view of a hysteresis loop of a magnetizationcurve of a magnetic field application bias film according to the presentinvention;

FIG. 2 is a circuit block diagram of a magnetic sensor according to afirst embodiment of the present invention;

FIG. 3A is an explanatory view of a magnetoresistive film of a firstmagnetoresistive sensor according to the first embodiment of the presentinvention viewed along a Y1-Y2 axis;

FIG. 3B is an explanatory view of a magnetoresistive film of a secondmagnetoresistive sensor according to the first embodiment of the presentinvention viewed along the Y1-Y2 axis;

FIG. 4A is an explanatory view of a film that includes an exchangecoupling film including an antiferromagnetic layer like a multilayerantiferromagnetic layer according to an embodiment of the presentinvention;

FIG. 4B is a depth profile of FIG. 4A;

FIG. 5 is an enlarged profile of a portion of the depth profile of FIG.4B;

FIG. 6 is a graph of the ratio of the Mn content to the Cr content(Mn/Cr ratio) based on FIG. 5, and the range in the horizontal axis isthe same as in FIG. 5;

FIG. 7A is an explanatory view of a magnetoresistive film of a firstmagnetoresistive sensor according to a modified example of the firstembodiment of the present invention;

FIG. 7B is an explanatory view of a magnetoresistive film of a firstmagnetoresistive sensor according to another modified example of thefirst embodiment of the present invention;

FIG. 8 is a circuit block diagram of a magnetic sensor according to asecond embodiment of the present invention;

FIG. 9A is an explanatory view of a magnetoresistive film of a firstmagnetoresistive sensor according to the second embodiment of thepresent invention viewed along a Y1-Y2 axis;

FIG. 9B is an explanatory view of a magnetoresistive film of a secondmagnetoresistive sensor according to the second embodiment of thepresent invention viewed along the Y1-Y2 axis; and

FIG. 10 is a graph of the temperature dependence of the intensity of anexchange coupling magnetic field Hex.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

FIG. 1 is an explanatory view of a hysteresis loop of a magnetizationcurve of an exchange coupling film with the pinning antiferromagneticlayer. A hysteresis loop of an M-H curve (magnetization curve) of a softmagnetic material is typically symmetric about a point of intersectionbetween an H axis and an M axis (magnetic field H=0 A/m, magnetizationM=0 A/m). As illustrated in FIG. 1, however, a hysteresis loop of theexchange coupling film shifts along the H axis depending on an exchangecoupling magnetic field Hex acting on a ferromagnetic layerexchange-coupled with the pinning antiferromagnetic layer. Themagnetization reversal of the pinning ferromagnetic layer of theexchange coupling film becomes more difficult even in an externalmagnetic field as the exchange coupling magnetic field Hex increases.Thus, a magnetic detector with such a pinning antiferromagnetic layerhas high resistance to a strong magnetic field.

Furthermore, the pinning antiferromagnetic layer has a higher blockingtemperature Tb than an antiferromagnetic layer formed of a knownantiferromagnetic material, such as IrMn or PtMn, as described inJapanese Unexamined Patent Application Publication No. 2006-527497, andcan maintain the exchange coupling magnetic field Hex, for example, evenat approximately 350° C. in an external magnetic field.

FIG. 2 is a circuit block diagram of a magnetic sensor (magneticdetector) according to a first embodiment of the present invention. FIG.3A is an explanatory view of a magnetoresistive film of a firstmagnetoresistive sensor according to the first embodiment of the presentinvention viewed along a Y1-Y2 axis; FIG. 3B is an explanatory view of amagnetoresistive film of a second magnetoresistive sensor according tothe first embodiment of the present invention viewed along the Y1-Y2axis.

As illustrated in FIG. 2, a magnetic sensor 100 includes a full-bridgecircuit FB composed of a first half-bridge circuit HB1 and a secondhalf-bridge circuit HB2 connected in parallel between a power supplyterminal Vdd and a ground terminal GND. The first half-bridge circuitHB1 is composed of a first magnetoresistive sensor M1 and a secondmagnetoresistive sensor M2 connected in series, and the secondhalf-bridge circuit HB2 is composed of the second magnetoresistivesensor M2 and the first magnetoresistive sensor M1 connected in series.The first magnetoresistive sensor M1 and the second magnetoresistivesensor M2 are located on the same substrate SB.

The differential output (OutX1)−(OutX2) between the output electricpotential (OutX1) of the first half-bridge circuit HB1 at a midpoint V1and the output electric potential (OutX2) of the second half-bridgecircuit HB2 at a midpoint V2 in the full-bridge circuit FB is obtainedas the detection output (detection output voltage) VXs along an X1-X2axis.

The first magnetoresistive sensor M1 includes a first magnetoresistivefilm MR1. The first magnetoresistive film MR1 is a giantmagnetoresistive film including a first pinned magnetic layer 15 withfixed magnetization in the X2 direction on the X1-X2 axis (in a fixedmagnetization direction P) and a first free magnetic layer 13 that iseasily magnetized along an external magnetic field H applied.

The first pinned magnetic layer 15 and a first pinning antiferromagneticlayer 16 constitute a first pinning exchange coupling film 511. Thefirst pinning antiferromagnetic layer 16 is located on the opposite sideof the first pinned magnetic layer 15 from the first free magnetic layer13 (on a Z1 side on a Z1-Z2 axis). An exchange coupling magnetic fieldHex is generated (at the interface) between the first pinned magneticlayer 15 and the first pinning antiferromagnetic layer 16 in the firstpinning exchange coupling film 511. The fixed magnetization direction Pof the first pinned magnetic layer 15 associated with the exchangecoupling magnetic field Hex is the X2 direction on the X1-X2 axis, asindicated by black arrows in FIGS. 2 and 3A.

The first free magnetic layer 13 and a first biasing antiferromagneticlayer 12 constitute a first biasing exchange coupling film 512. Thefirst biasing antiferromagnetic layer 12 is located on the opposite sideof the first free magnetic layer 13 from the first pinned magnetic layer15 (on the Z2 side on the Z1-Z2 axis). In the first biasing exchangecoupling film 512, an exchange coupling magnetic field Hex in the Y1direction on the Y1-Y2 axis is generated (at the interface) between thefirst biasing antiferromagnetic layer 12 and the first free magneticlayer 13. As indicated by white arrows in FIG. 2 and a backward arrow inthe drawing of FIG. 3A, due to the exchange coupling magnetic field Hex,a bias magnetic field in the Y1 direction on the Y1-Y2 axis (in the biasapplication direction F) is applied to the first free magnetic layer 13in the direction of the exchange coupling magnetic field Hex. In theabsence of the external magnetic field H, the bias magnetic fieldmagnetizes the first free magnetic layer 13 in the bias applicationdirection F.

The second magnetoresistive sensor M2 includes a second magnetoresistivefilm MR2. The second magnetoresistive film MR2 is a giantmagnetoresistive film including a second pinned magnetic layer 25 withfixed magnetization in the X1 direction on the X1-X2 axis (in the fixedmagnetization direction P) and a second free magnetic layer 23 that iseasily magnetized along the external magnetic field H applied.

The second pinned magnetic layer 25 and a second pinningantiferromagnetic layer 26 constitute a second pinning exchange couplingfilm 521. The second pinning antiferromagnetic layer 26 is located onthe opposite side of the second pinned magnetic layer 25 from the secondfree magnetic layer 23 (on the Z1 side on the Z1-Z2 axis). An exchangecoupling magnetic field Hex is generated (at the interface) between thesecond pinned magnetic layer 25 and the second pinning antiferromagneticlayer 26 in the second pinning exchange coupling film 521. The fixedmagnetization direction P of the second pinned magnetic layer 25associated with the exchange coupling magnetic field Hex is the X1direction on the X1-X2 axis, as indicated by black arrows in FIGS. 2 and3B. The fixed magnetization direction P of the first pinned magneticlayer 15 is coaxial with but opposite to, that is, antiparallel to thefixed magnetization direction P of the second pinned magnetic layer 25.

The second free magnetic layer 23 and a second biasing antiferromagneticlayer 22 constitute a second biasing exchange coupling film 522. Thesecond biasing antiferromagnetic layer 22 is located on the oppositeside of the second free magnetic layer 23 from the second pinnedmagnetic layer 25 (on the Z2 side on the Z1-Z2 axis). In the secondbiasing exchange coupling film 522, an exchange coupling magnetic fieldHex in the Y1 direction on the Y1-Y2 axis is generated (at theinterface) between the second biasing antiferromagnetic layer 22 and thesecond free magnetic layer 23. As indicated by white arrows in FIG. 2and a backward arrow in the drawing of FIG. 3B, due to the exchangecoupling magnetic field Hex, a bias magnetic field in the Y1 directionon the Y1-Y2 axis (in the bias application direction F) is applied tothe second free magnetic layer 23 in the direction of the exchangecoupling magnetic field Hex. In the absence of the external magneticfield H, the bias magnetic field magnetizes the second free magneticlayer 23 in the bias application direction F. The direction of a biasmagnetic field applied to the first free magnetic layer 13 (the biasapplication direction F) is coaxial with and the same as, that is,parallel to the direction of a bias magnetic field applied to the secondfree magnetic layer 23 (the bias application direction F).

Because the direction of the exchange coupling magnetic field Hex in thefirst pinning exchange coupling film 511 is nonparallel to (morespecifically, when viewed along the Z1-Z2 axis (when viewed in thestacking direction), perpendicular to) the direction of the exchangecoupling magnetic field Hex in the first biasing exchange coupling film512, the fixed magnetization direction P of the first pinned magneticlayer 15 is perpendicular to the bias application direction F of thefirst free magnetic layer 13 when viewed along the Z1-Z2 axis. Becausethe direction of the exchange coupling magnetic field Hex in the secondpinning exchange coupling film 521 is nonparallel to (more specifically,when viewed along the Z1-Z2 axis, perpendicular to) the direction of theexchange coupling magnetic field Hex in the second biasing exchangecoupling film 522, the fixed magnetization direction P of the secondpinned magnetic layer 25 is perpendicular to the bias applicationdirection F of the second free magnetic layer 23 when viewed along theZ1-Z2 axis. Application of the external magnetic field H to the magneticsensor 100 along the X1-X2 axis rotates the magnetization direction ofthe first free magnetic layer 13 and the magnetization direction of thesecond free magnetic layer 23 in the direction of the external magneticfield H, and the resistance of the first magnetoresistive sensor M1 andthe resistance of the second magnetoresistive sensor M2 depend on themagnetization direction of the pinned magnetic layer and themagnetization direction of the free magnetic layer.

Because the fixed magnetization direction P of the first pinned magneticlayer 15 is antiparallel to the fixed magnetization direction P of thesecond pinned magnetic layer 25, the external magnetic field H in the X2direction on the X1-X2 axis reduces the resistance of the firstmagnetoresistive sensor M1 and increases the resistance of the secondmagnetoresistive sensor M2. Thus, the differential output(OutX1)−(OutX2) is positive. In contrast, the external magnetic field Hin the X1 direction on the X1-X2 axis increases the resistance of thefirst magnetoresistive sensor M1 and reduces the resistance of thesecond magnetoresistive sensor M2. Thus, the differential output(OutX1)−(OutX2) is negative. Thus, the direction of the externalmagnetic field H can be determined from the polarity of differentialoutput (OutX1)−(OutX2).

As described above, in the magnetic sensor 100, the exchange couplingmagnetic field Hex defines magnetization in the three directions: thefixed magnetization direction P in the first magnetoresistive sensor M1(the X2 direction on the X1-X2 axis), the fixed magnetization directionP in the second magnetoresistive sensor M2 (the X1 direction on theX1-X2 axis), and the bias magnetic field direction in the firstmagnetoresistive sensor M1 and the second magnetoresistive sensor M2(the bias application direction F, the Y1 direction on the Y1-Y2 axis).To achieve magnetization in the three directions, the magnetic sensor100 includes three materials with different blocking temperatures Tbs asantiferromagnetic layers involved in the generation of the exchangecoupling magnetic field Hex, as described below.

More specifically, each of the blocking temperature Tbf1 of the firstpinning antiferromagnetic layer 16 and the blocking temperature Tbf2 ofthe second pinning antiferromagnetic layer 26 is higher than theblocking temperature Tb1 of a first biasing antiferromagnetic layer 12and the blocking temperature Tb2 of a second biasing antiferromagneticlayer 22. The blocking temperature Tb1 of the first biasingantiferromagnetic layer 12 is higher than the blocking temperature Tb2of the second biasing antiferromagnetic layer 22. Thus, differentblocking temperatures Tbs can result in exchange coupling magneticfields in the three different directions.

Table 1 shows a specific example of the first magnetoresistive film MR1.In Table 1, the leftmost column indicates each layer of the firstmagnetoresistive film MR1, and the second column from the rightindicates an example of the material of each layer. The numerical valuesin the rightmost column indicate the thickness of each layer (unit:angstrom (A)). The first magnetoresistive film MR1 is a giantmagnetoresistive film, and a nonmagnetic material layer 14 between thefirst pinned magnetic layer 15 and the first free magnetic layer 13constitutes a spin-valve structure.

TABLE 1 17 Protective layer Ta 90 16 First pinning antiferromagneticlayer 51PtCr 280 50PtMn 20 15 First pinned Ferromagnetic layer 60FeCo 17magnetic layer Nonmagnetic intermediate layer Ru 3.6 Ferromagnetic layer90CoFe 24 14 Nonmagnetic material layer Cu 30 13 First freeFerromagnetic layer 90CoFe 10 magnetic layer Ferromagnetic layer81.5NiFe 80 Ferromagnetic layer 90CoFe 10 12 First biasingantiferromagnetic layer 50PtMn 300 11 Underlayer NiFeCr 42

An underlayer 11 on the substrate SB may be formed of a NiFeCr alloy (anickel-iron-chromium alloy), Cr, or Ta. In Table 1, the underlayer 11 isa NiFeCr alloy layer 42 angstroms in thickness.

The first biasing antiferromagnetic layer 12 is located on theunderlayer 11. In Table 1, the first biasing antiferromagnetic layer 12is a Pt_(50at%)Mn_(50at%) layer 300 angstroms in thickness. The firstbiasing antiferromagnetic layer 12 is annealed for ordering and forms,together with the first free magnetic layer 13, the first biasingexchange coupling film 512 by exchange coupling. An exchange couplingmagnetic field Hex is generated (at the interface) between the firstbiasing antiferromagnetic layer 12 and the first free magnetic layer 13.The first biasing antiferromagnetic layer 12 has a blocking temperatureTb1 of approximately 400° C. Thus, the exchange coupling magnetic fieldHex is maintained even when the first biasing exchange coupling film 512is heated to approximately 300° C. In the formation of an alloy layer,such as the first biasing antiferromagnetic layer 12, metals for formingthe alloy (Pt and Mn for the first biasing antiferromagnetic layer 12)may be simultaneously or alternately supplied. For example, metals forforming the alloy may be simultaneously sputtered, or different types ofmetal films may be alternately stacked. Simultaneous supply of metalsfor forming the alloy is sometimes preferred rather than alternatesupply to increase the exchange coupling magnetic field Hex.

The first free magnetic layer 13 is located on the first biasingantiferromagnetic layer 12. The first free magnetic layer 13 may beformed of a CoFe alloy (a cobalt-iron alloy) or a NiFe alloy (anickel-iron alloy) and may have a monolayer structure, a layeredstructure, or a layered ferri structure. In Table 1, aCo_(90at%)Fe_(10at%) layer 10 angstroms in thickness, aNi_(81.5at%)Fe_(18.5at%) layer 80 angstroms in thickness, and aCo_(90at%)Fe_(10at%) layer 10 angstroms in thickness are located on thefirst biasing antiferromagnetic layer 12 in this order to constitute thefirst free magnetic layer 13.

The nonmagnetic material layer 14 is located on the first free magneticlayer 13. The nonmagnetic material layer 14 can be formed of Cu (copper)or the like. In Table 1, the nonmagnetic material layer 14 is a Cu layer30 angstroms in thickness.

The first pinned magnetic layer 15 is located on the nonmagneticmaterial layer 14. The first pinned magnetic layer 15 is formed of aferromagnetic CoFe alloy (a cobalt-iron alloy). The coercive force ofthe CoFe alloy increases with the Fe content. The first pinned magneticlayer 15 contributes to the spin-valve giant magnetoresistance effect.The fixed magnetization direction P of the first pinned magnetic layer15 is the sensitivity axis direction of the first magnetoresistivesensor M1. To increase the resistance of the first pinning exchangecoupling film 511 to a strong magnetic field, the first pinned magneticlayer 15 preferably has a self-pinning structure, as shown in Table 1.In Table 1, a Co_(90at%)Fe_(10at%) ferromagnetic layer 24 angstroms inthickness, a Ru nonmagnetic intermediate layer 3.6 angstroms inthickness, and a Fe_(60at%)Co_(40at%) ferromagnetic layer 17 angstromsin thickness are located on the nonmagnetic material layer 14 in thisorder.

The first pinning antiferromagnetic layer 16 is located on theFe_(60at%)Co_(40at%) ferromagnetic layer 17 angstroms in thicknessconstituting the first pinned magnetic layer 15. A Pt_(50at%)Mn_(50at%)layer 20 angstroms in thickness and a Pt_(51at%)Cr_(49at%) layer 280angstroms in thickness are layered on the first pinned magnetic layer 15in this order to form the first pinning antiferromagnetic layer 16.

The first pinning antiferromagnetic layer 16 is annealed for orderingand forms, together with the first pinned magnetic layer 15, the firstpinning exchange coupling film 511. An exchange coupling magnetic fieldHex is generated (at the interface) between the first pinningantiferromagnetic layer 16 and the first pinned magnetic layer 15. Thefirst pinning antiferromagnetic layer 16 has a blocking temperature Tbf1of approximately 500° C. Thus, the exchange coupling magnetic field Hexis maintained even when the first pinning exchange coupling film 511 isheated to approximately 400° C.

A protective layer 17 is formed on the first pinning antiferromagneticlayer 16. The protective layer 17 can be formed of Ta (tantalum) or thelike. In Table 1, a Ta layer 90 angstroms in thickness is formed.

Table 2 shows a specific example of the second magnetoresistive filmMR2. In Table 2, the leftmost column indicates each layer of the secondmagnetoresistive film MR2, and the second column from the rightindicates an example of the material of each layer. The numerical valuesin the rightmost column indicate the thickness of each layer (unit:angstrom (Å)). The second magnetoresistive film MR2 is a giantmagnetoresistive film, and a nonmagnetic material layer 24 between thesecond pinned magnetic layer 25 and the second free magnetic layer 23constitutes a spin-valve structure.

TABLE 2 27 Protective layer Ta 90 26 Second pinning antiferromagneticlayer 51PtCr 280 50PtMn 20 25 Second pinned Ferromagnetic layer 60FeCo17 magnetic layer Nonmagnetic intermediate layer Ru 3.6 Ferromagneticlayer 90CoFe 24 24 Nonmagnetic material layer Cu 30 23 Second freeFerromagnetic layer 90CoFe 10 magnetic layer Ferromagnetic layer81.5NiFe 80 Ferromagnetic layer 90CoFe 10 22 Second biasingantiferromagnetic layer 20IrMn 80 21 Underlayer NiFeCr 42

An underlayer 21, the second free magnetic layer 23, the nonmagneticmaterial layer 24, the second pinned magnetic layer 25, and a protectivelayer 27 have the same compositions as the underlayer 11, the first freemagnetic layer 13, the nonmagnetic material layer 14, the first pinnedmagnetic layer 15, and the protective layer 17, respectively, and arenot described here.

The second biasing antiferromagnetic layer 22 is an Ir_(20at%)Mn_(80at%)layer 80 angstroms in thickness. The second biasing antiferromagneticlayer 22 and the second free magnetic layer 23 form the second biasingexchange coupling film 522 by exchange coupling and generate an exchangecoupling magnetic field Hex (at the interface) between the secondbiasing antiferromagnetic layer 22 and the second free magnetic layer23. The second biasing antiferromagnetic layer 22 has a blockingtemperature Tb2 of approximately 300° C., which is lower than theblocking temperature Tb1 of the first biasing antiferromagnetic layer 12(approximately 400° C.).

A Pt_(50at%)Mn_(50at%) layer 20 angstroms in thickness and aPt_(51at%)Cr_(49at%) layer 280 angstroms in thickness are layered on thesecond pinned magnetic layer 25 in this order to form the second pinningantiferromagnetic layer 26. The second pinning antiferromagnetic layer26 is annealed for ordering and forms, together with the second pinnedmagnetic layer 25, the second pinning exchange coupling film 521 byexchange coupling. An exchange coupling magnetic field Hex is generated(at the interface) between the second pinning antiferromagnetic layer 26and the second pinned magnetic layer 25. The second pinningantiferromagnetic layer 26 has a blocking temperature Tbf2 ofapproximately 500° C. Thus, the exchange coupling magnetic field Hex ismaintained even when the second pinning exchange coupling film 521 isheated to approximately 400° C.

Thus, the magnetic sensor 100 includes the three antiferromagneticlayers with different blocking temperatures Tbs. In the magnetic sensor100 produced by forming and heating each layer as described below,therefore, each magnetoresistive sensor (the first magnetoresistivesensor M1, the second magnetoresistive sensor M2) can have a fixedmagnetization direction P and a bias application direction F inpredetermined directions.

First, the fixed magnetization axis setting step is performed. In thisstep, the first pinning antiferromagnetic layer 16 and the secondpinning antiferromagnetic layer 26 are ordered by heat treatment. Anyordering temperature may be used. The ordering temperature is typicallyslightly lower than the blocking temperature Tbf1 of the first pinningantiferromagnetic layer 16 and the blocking temperature Tbf2 of thesecond pinning antiferromagnetic layer 26, for example, approximately300° C. to 400° C. The heat-treatment time may also be any time,provided that the ordering can be achieved. For example, theheat-treatment time may be, but is limited to, one hour or more, morespecifically approximately five hours.

Thus, the first pinning antiferromagnetic layer 16 and the secondpinning antiferromagnetic layer 26 are ordered, and an exchange couplingmagnetic field Hex is generated in the first pinning exchange couplingfilm 511 and the second pinning exchange coupling film 521. In theordering, the magnetization direction of the first pinningantiferromagnetic layer 16 is adjusted to the magnetization direction ofthe first pinned magnetic layer 15. Thus, the exchange coupling magneticfield Hex in the first pinning exchange coupling film 511 is generatedin the magnetization direction of the first pinned magnetic layer 15. Inthe ordering, the magnetization direction of the second pinningantiferromagnetic layer 26 is adjusted to the magnetization direction ofthe second pinned magnetic layer 25. Thus, the exchange couplingmagnetic field Hex in the second pinning exchange coupling film 521 isgenerated in the magnetization direction of the second pinned magneticlayer 25.

Thus, setting the magnetization direction of the first pinned magneticlayer 15 in the X2 direction on the X1-X2 axis during the formation ofthe first pinned magnetic layer 15 and setting the magnetizationdirection of the second pinned magnetic layer 25 in the X1 direction onthe X1-X2 axis during the formation of the second pinned magnetic layer25 can make the fixed magnetization direction P of the first pinnedmagnetic layer 15 coaxial with (more specifically, antiparallel to) thefixed magnetization direction P of the second pinned magnetic layer 25in the fixed magnetization axis setting step.

If the magnetization direction of the first free magnetic layer 13 incontact with the first biasing antiferromagnetic layer 12 is preventedfrom being adjusted, the magnetization direction of the first biasingantiferromagnetic layer 12 is not adjusted in the fixed magnetizationaxis setting step. Likewise, if the magnetization direction of thesecond free magnetic layer 23 in contact with the second biasingantiferromagnetic layer 22 is prevented from being adjusted, themagnetization direction of the second biasing antiferromagnetic layer 22can be prevented from being adjusted in the fixed magnetization axissetting step.

Subsequently, in the first bias magnetic field setting step, heattreatment is performed at a temperature lower than the blockingtemperature Tbf1 of the first pinning antiferromagnetic layer 16 and theblocking temperature Tbf2 of the second pinning antiferromagnetic layer26 (for example, 350° C.). In the heat treatment, application of anexternal magnetic field in the Y1 direction on the Y1-Y2 axis generatesan exchange coupling magnetic field Hex in the external magnetic fielddirection between the first biasing antiferromagnetic layer 12 and thefirst free magnetic layer 13 and generates a bias magnetic field appliedto the first free magnetic layer 13 in the Y1 direction on the Y1-Y2axis (in the bias application direction F). The bias applicationdirection F of the first free magnetic layer 13 is nonparallel to, morespecifically when viewed along the Z1-Z2 axis perpendicular to, thefixed magnetization direction P of the first pinned magnetic layer 15.

The heat-treatment temperature in the first bias magnetic field settingstep is lower than the blocking temperature Tbf1 of the first pinningantiferromagnetic layer 16 and the blocking temperature Tbf2 of thesecond pinning antiferromagnetic layer 26. Thus, the fixed magnetizationdirection P in the first pinned magnetic layer 15 and the fixedmagnetization direction P in the second pinned magnetic layer 25 are notchanged to the direction of the applied external magnetic field and aremaintained.

Finally, in the second bias magnetic field setting step, heat treatmentis performed at a temperature lower than the blocking temperature Tb1 ofthe first biasing antiferromagnetic layer 12 (for example, 300° C.). Inthe heat treatment, application of an external magnetic field in the Y1direction on the Y1-Y2 axis generates an exchange coupling magneticfield Hex in the external magnetic field direction between the secondbiasing antiferromagnetic layer 22 and the second free magnetic layer 23and generates a bias magnetic field applied to the second free magneticlayer 23 in the Y1 direction on the Y1-Y2 axis (in the bias applicationdirection F). The bias application direction F of the second freemagnetic layer 23 is nonparallel to, more specifically when viewed alongthe Z1-Z2 axis perpendicular to, the fixed magnetization direction P ofthe second pinned magnetic layer 25.

The heat-treatment temperature in the second bias magnetic field settingstep is lower than the blocking temperature Tbf1 of the first pinningantiferromagnetic layer 16, the blocking temperature Tbf2 of the secondpinning antiferromagnetic layer 26, and the blocking temperature Tb1 ofthe first biasing antiferromagnetic layer 12. Thus, the fixedmagnetization direction P in the first pinned magnetic layer 15, thefixed magnetization direction P in the second pinned magnetic layer 25,and the direction of a bias magnetic field applied to the first freemagnetic layer 13 (the bias application direction F) are not changed tothe direction of the magnetic field applied and are maintained.

Thus, when the magnetic sensor 100 includes the three antiferromagneticlayers with different blocking temperatures Tbs, the above step cangenerate an exchange coupling magnetic field Hex in any direction in theferromagnetic layers exchange-coupled with the antiferromagnetic layers(the first pinned magnetic layer 15, the second pinned magnetic layer25, the first free magnetic layer 13, and the second free magnetic layer23).

A multilayer antiferromagnetic layer for use in the first pinningantiferromagnetic layer 16 of the first pinning exchange coupling film511 and the second pinning antiferromagnetic layer 26 of the secondpinning exchange coupling film 521 is described in detail below.

A multilayer antiferromagnetic layer according to an embodiment of thepresent invention includes an X(Cr—Mn) layer containing one or two ormore elements X selected from the group consisting of platinum groupelements and Ni and containing Mn and Cr. Each of the first pinningantiferromagnetic layer 16 and the second pinning antiferromagneticlayer 26 is a Pt(Cr—Mn) layer because the element X is Pt. The Pt(Cr—Mn)layer has a first region located relatively near the ferromagneticlayers (the first pinned magnetic layer 15, the second pinned magneticlayer 25) exchange-coupled with the antiferromagnetic layers (the firstpinning antiferromagnetic layer 16, the second pinning antiferromagneticlayer 26) and a second region located relatively far from theferromagnetic layers (the first pinned magnetic layer 15, the secondpinned magnetic layer 25).

The first region has a higher Mn content than the second region. ThePt(Cr—Mn) layer with such a structure is formed by annealing a PtMnlayer and a PtCr layer stacked. The content distribution of theconstituent elements in the depth direction (depth profile) can bedetermined by surface analysis during sputtering.

FIG. 4A is an explanatory view of a film 60 that includes an exchangecoupling film 55 including an antiferromagnetic layer 64 like amultilayer antiferromagnetic layer according to an embodiment of thepresent invention. FIG. 4B is a depth profile of the film 60. Asillustrated in FIG. 4A, the film 60 has the following layered structure.Each numerical value in parentheses indicates the thickness (angstroms).An IrMn layer 641, a PtMn layer 642, and a PtCr layer 643 are layered onthe pinned magnetic layer 63 in this order to form the antiferromagneticlayer 64.

Substrate/underlayer 61: NiFeCr (40)/nonmagnetic material layer 62: [Cu(40)/Ru (20)]/pinned magnetic layer 63: Co_(40at%)Fe_(60at%)(20)/antiferromagnetic layer 64 [IrMn layer 641: Ir_(22at%)Mn_(78at%)(10)/PtMn layer 642: Pt_(50at%)Mn_(50at%) (16)/PtCr layer 643:Pt_(51at%)Cr_(49at%) (300)]/protective layer 65: Ta (100)

The depth profile in FIG. 4B was measured in the film 60 with the abovestructure ordered by annealing in a 15-kOe magnetic field at 350° C. for20 hours.

More specifically, the depth profile in FIG. 4B is the distribution ofthe Pt, Ir, Cr, and Mn contents in the depth direction obtained by asurface analysis with an Auger electron spectrometer during argonsputtering on the protective layer 65. The argon sputtering rate was 1.1nm/min on a SiO₂ basis.

FIG. 5 is an enlarged view of FIG. 4B. In both FIG. 4B and FIG. 5, todetermine the depth positions of the pinned magnetic layer 63 and thenonmagnetic material layer 62, the depth profile also includes thedistribution of the Co content (one of the constituent elements of thepinned magnetic layer 63) and the distribution of the Ru content (anelement constituting the antiferromagnetic layer 64 side of thenonmagnetic material layer 62).

FIG. 4B shows that the antiferromagnetic layer 64 has a thickness ofapproximately 30 nm and includes an X(Cr—Mn) layer containing Pt and Iras one or two or more elements X selected from the group consisting ofplatinum group elements and Ni and containing Mn and Cr, morespecifically a (Pt—Ir) (Cr—Mn) layer. The X(Cr—Mn) layer (the(Pt—Ir)(Cr—Mn) layer) has a first region R1 located relatively near thepinned magnetic layer 63 and a second region R2 located relatively farfrom the pinned magnetic layer 63. The first region R1 has a higher Mncontent than the second region R2. Such a structure can be formed bystacking an XCr layer and an XMn layer to form a layered body andannealing the layered body as described above.

FIG. 6 is a graph of the ratio of the Mn content to the Cr content(Mn/Cr ratio) calculated from the Mn content and the Cr content at eachdepth in the depth profile. The range in the horizontal axis is the sameas in FIG. 5. On the basis of FIG. 6, in the present specification, thedepth at which the Mn/Cr ratio is 0.1 is the boundary between the firstregion R1 and the second region R2. More specifically, in theantiferromagnetic layer 64, a region located near the pinned magneticlayer 63 and having a Mn/Cr ratio of 0.1 or more is defined as the firstregion R1, and a region other than the first region in theantiferromagnetic layer 64 is defined as the second region R2. On thebasis of this definition, the boundary between the first region R1 andthe second region R2 is located at a depth of approximately 44.5 nm inthe depth profile of FIG. 4B.

Not only a high Mn/Cr ratio has an influence on the intensity of theexchange coupling magnetic field Hex, but also a higher Mn/Cr ratiotends to result in a higher positive Hex/Hc value (Hc: coercive force).More specifically, the first region R1 preferably includes a portionwith a Mn/Cr ratio of 0.3 or more, more preferably 0.7 or more,particularly preferably 1 or more.

Due to such a relatively high Mn content of the first region R1, theexchange coupling film 55 can generate a high exchange coupling magneticfield Hex. On the other hand, due to a low Mn content and acorrespondingly high Cr content of the second region R2, theantiferromagnetic layer 64 has a high blocking temperature Tb. Thus, theexchange coupling film 55 can maintain the exchange coupling magneticfield Hex even in a high-temperature environment. Although the PtMnlayer 642 and the IrMn layer 641 are stacked on the pinned magneticlayer 63 of the PtCr layer 643 in this embodiment, the present inventionis not limited to the embodiment. An X⁰Mn layer located nearer theferromagnetic layer than the PtCr layer 643 (wherein X⁰ denotes one ortwo or more elements selected from the group consisting of platinumgroup elements and Ni) may be located on the pinned magnetic layer 63.In the first pinning exchange coupling film 511, the X⁰Mn layer is aPtMn layer (50PtMn in Table 1).

FIG. 7A is an explanatory view of a multilayer antiferromagnetic layeraccording to another embodiment. The multilayer antiferromagnetic layeraccording to the present embodiment is different in the structure oflayers stacked to form the antiferromagnetic layer from theantiferromagnetic layers according to the above embodiments of thepresent invention (the first pinning antiferromagnetic layer 16, thesecond pinning antiferromagnetic layer 26, and the antiferromagneticlayer 64). As illustrated in FIG. 7A, an antiferromagnetic layer 74 inan exchange coupling film 56 of a film 70 has an alternately layeredstructure composed of three layers consisting of X¹Cr layers 74A and anX²Mn layer 74B (wherein X¹ and X² independently denote one or two ormore elements selected from the group consisting of platinum groupelements and Ni, and X¹ and X² may be the same or different). Theselayers are formed by sputtering or CVD, for example. After itsformation, the antiferromagnetic layer 74 is annealed for ordering andis exchange-coupled with a pinned magnetic layer 73 located on anonmagnetic material layer 72 located on an underlayer 71, therebygenerating an exchange coupling magnetic field Hex in the pinnedmagnetic layer 73.

In FIG. 7A, the antiferromagnetic layer 74 includes three-layerstructure of the X¹Cr layer 74A/X²Mn layer 74B/X¹Cr layer 74A in contactwith the pinned magnetic layer 73 as one embodiment of an alternatelylayered structure of three layers or more composed of the X¹Cr layer 74Aand the X²Mn layer 74B. The X¹Cr layer 74A and the X²Mn layer 74B may bereplaced with each other, and the three-layer structure may be the X²Mnlayer 74B/X¹Cr layer 74A/X²Mn layer 74B. In this three-layer structure,the X²Mn layer 74B is in contact with the pinned magnetic layer 73. Theantiferromagnetic layer 74 composed of four or more layers are describedlater.

In the case where the X¹Cr layer 74A is located nearest the pinnedmagnetic layer 73, the thickness D1 of the X¹Cr layer 74A in contactwith a protective layer 75 is preferably larger than the thickness D3 ofthe X¹Cr layer 74A in contact with the pinned magnetic layer 73 in orderto increase the exchange coupling magnetic field Hex. The thickness D1of the X1Cr layer 74A in the antiferromagnetic layer 74 is alsopreferably larger than the thickness D2 of the X²Mn layer 74B. The ratioof the thickness D1 to the thickness D2 (D1:D2) preferably ranges from5:1 to 100:1, more preferably 10:1 to 50:1. The ratio of the thicknessD1 to the thickness D3 (D1:D3) preferably ranges from 5:1 to 100:1, morepreferably 10:1 to 50:1.

In the case of the three-layer structure of the X²Mn layer 74B/X1Crlayer 74A/X²Mn layer 74B where the X²Mn layer 74B is located nearest thepinned magnetic layer 73, the thickness D3 of the X²Mn layer 74B locatednearest the pinned magnetic layer 73 may be the same as the thickness D1of the X²Mn layer 74B in contact with the protective layer 75.

To increase the exchange coupling magnetic field Hex, X¹ in the X¹Crlayer 74A is preferably Pt, and X² in the X²Mn layer 74B is preferablyPt or Ir, more preferably Pt. In the case where the X¹Cr layer 74A is aPtCr layer, Pt_(X)Cr_(100-X) (wherein X denotes 45 to 62 atomic percent)is preferred, and Pt_(X)Cr_(100-X) (wherein X denotes 50 to 57 atomicpercent) is more preferred. From the same perspective, the X²Mn layer74B is preferably a PtMn layer.

FIG. 7B is an explanatory view of a multilayer antiferromagnetic layeraccording to a modified example of another embodiment. In the presentembodiment, layers with the same function as in the film 70 illustratedin FIG. 7A are denoted by the same reference numerals and letters andare not described here. In a film 70A in FIG. 7B, the pinned magneticlayer 73 and an antiferromagnetic layer 741 constitute an exchangecoupling film 57.

Unlike the exchange coupling film 56 in FIG. 7A, the exchange couplingfilm 57 in FIG. 7B includes four or more layers in the antiferromagneticlayer 741 and has a unit layered portion including a plurality of unitseach composed of the X¹Cr layer 74A and the X²Mn layer 74B. In FIG. 7B,the exchange coupling film 57 includes unit layered portions 4U1 to 4Un(n is an integer of 2 or more). The unit layered portion 4U1 is composedof an X¹Cr layer 74A1 and an X²Mn layer 74B1, and the unit layeredportion 4Un is composed of an X¹Cr layer 74An and an X²Mn layer 74Bn.

In the unit layered portions 4U1 to 4Un, the X¹Cr layers 74A1 to 74Anhave the same thickness D1, and the X²Mn layers 74B1 to 74Bn have thesame thickness D2. A high exchange coupling magnetic field Hex in thepinned magnetic layer 73 of the exchange coupling film 57 and betterhigh-temperature stability of the antiferromagnetic layer 741 can beachieved by stacking the unit layered portions 4U1 to 4Un each havingthe same structure and annealing the layered body.

Although the antiferromagnetic layer 741 in FIG. 7B is composed of theunit layered portions 4U1 to 4Un and the X¹Cr layer 74A in contact withthe pinned magnetic layer 73, the antiferromagnetic layer 741 may becomposed only of the unit layered portions 4U1 to 4Un. In theantiferromagnetic layer 741 formed of a layered body composed only ofthe unit layered portions 4U1 to 4Un, the X²Mn layer 74B1 is in contactwith the pinned magnetic layer 73.

The number of layers in the unit layered portions 4U1 to 4Un can bedetermined according to the size of the antiferromagnetic layer 741 andthe thicknesses D1 and D2. For example, for a thickness D1 in the rangeof 5 to 15 angstroms and a thickness D2 in the range of 30 to 40angstroms, the number of layers preferably ranges from 3 to 15, morepreferably 5 to 12, in order to increase the exchange coupling magneticfield Hex in a high-temperature environment.

FIG. 8 is a circuit block diagram of a magnetic sensor (magneticdetector) according to a second embodiment of the present invention.FIG. 9A is an explanatory view of a magnetoresistive film of a firstmagnetoresistive sensor according to the second embodiment of thepresent invention viewed along the Y1-Y2 axis. FIG. 9B is an explanatoryview of a magnetoresistive film of a second magnetoresistive sensoraccording to the second embodiment of the present invention viewed alongthe Y1-Y2 axis.

In the present embodiment, components with the same function as in themagnetic sensor 100 illustrated in FIGS. 2 and 3 are denoted by the samereference numerals and letters and are not described here.

As illustrated in FIG. 8, like the magnetic sensor 100, a magneticsensor 101 includes the full-bridge circuit FB composed of the firsthalf-bridge circuit HB1 and the second half-bridge circuit HB2, and thefirst magnetoresistive sensor M1 and the second magnetoresistive sensorM2 in each half-bridge circuit are located on the same substrate SB. Inthe magnetic sensor 101, each magnetoresistive sensor has a fixedmagnetization direction P and a bias application direction F differentfrom those of the magnetic sensor 100.

The first magnetoresistive sensor M1 includes the first magnetoresistivefilm MR1. The first magnetoresistive film MR1 is a tunnelingmagnetoresistive film including a first pinned magnetic layer 34 withfixed magnetization in the Y1 direction on the Y1-Y2 axis (in the fixedmagnetization direction P) and a first free magnetic layer 36 that iseasily magnetized along an external magnetic field H applied.

The first pinned magnetic layer 34 and a first pinning antiferromagneticlayer 33 constitute a first pinning exchange coupling film 532. Thefirst pinning antiferromagnetic layer 33 is located on the opposite sideof the first pinned magnetic layer 34 from the first free magnetic layer36 (on a Z2 side on a Z1-Z2 axis). An exchange coupling magnetic fieldHex is generated (at the interface) between the first pinned magneticlayer 34 and the first pinning antiferromagnetic layer 33. The fixedmagnetization direction P of the first pinned magnetic layer 34associated with the exchange coupling magnetic field Hex is the Y1direction on the Y1-Y2 axis, as indicated by black arrows in FIG. 8 andbackward arrows in FIGS. 9A and 9B.

The first free magnetic layer 36 and a first biasing antiferromagneticlayer 37 constitute a first biasing exchange coupling film 531. Thefirst biasing antiferromagnetic layer 37 is located on the opposite sideof the first free magnetic layer 36 from the first pinned magnetic layer34 (on the Z1 side on the Z1-Z2 axis). An exchange coupling magneticfield Hex is generated (at the interface) between the first biasingantiferromagnetic layer 37 and the first free magnetic layer 36 on theX-Y plane at 45 degrees from the Y1 direction on the Y1-Y2 axis towardthe X2 direction on the X1-X2 axis (in the X2-Y1 direction). Asindicated by white arrows in FIGS. 8 and 9A, due to the exchangecoupling magnetic field Hex, a bias magnetic field in the X2-Y1direction (in the bias application direction F) is applied to the firstfree magnetic layer 36 in the direction of the exchange couplingmagnetic field Hex. In the absence of the external magnetic field H, thebias magnetic field magnetizes the first free magnetic layer 36 in thebias application direction F.

The second magnetoresistive sensor M2 includes the secondmagnetoresistive film MR2. The second magnetoresistive film MR2 is atunneling magnetoresistive film including a second pinned magnetic layer44 with fixed magnetization in the Y1 direction on the Y1-Y2 axis (inthe fixed magnetization direction P) and a second free magnetic layer 46that is easily magnetized along an external magnetic field H applied.

The second pinned magnetic layer 44 and a second pinningantiferromagnetic layer 43 constitute a second pinning exchange couplingfilm 542. The second pinning antiferromagnetic layer 43 is located onthe opposite side of the second pinned magnetic layer 44 from the secondfree magnetic layer 46 (on the Z2 side on the Z1-Z2 axis). An exchangecoupling magnetic field Hex is generated (at the interface) between thesecond pinned magnetic layer 44 and the second pinning antiferromagneticlayer 43. The fixed magnetization direction P of the second pinnedmagnetic layer 44 associated with the exchange coupling magnetic fieldHex is the Y1 direction on the Y1-Y2 axis, as indicated by black arrowsin FIG. 8 and backward arrows in FIGS. 9A and 9B. The fixedmagnetization direction P of the first pinned magnetic layer 34 iscoaxial with and the same as (parallel to) the fixed magnetizationdirection P of the second pinned magnetic layer 44.

The second free magnetic layer 46 and a second biasing antiferromagneticlayer 47 constitute a second biasing exchange coupling film 541. Thesecond biasing antiferromagnetic layer 47 is located on the oppositeside of the second free magnetic layer 46 from the second pinnedmagnetic layer 44 (on the Z1 side on the Z1-Z2 axis). An exchangecoupling magnetic field Hex is generated (at the interface) between thesecond biasing antiferromagnetic layer 47 and the second free magneticlayer 46 on the X-Y plane at 45 degrees from the Y1 direction on theY1-Y2 axis toward the X1 direction on the X1-X2 axis (in the X1-Y1direction). As indicated by white arrows in FIGS. 8 and 9B, due to theexchange coupling magnetic field Hex, a bias magnetic field in the X1-Y1direction (in the bias application direction F) is applied to the secondfree magnetic layer 46 in the direction of the exchange couplingmagnetic field Hex. In the absence of the external magnetic field H, thebias magnetic field magnetizes the second free magnetic layer 46 in thebias application direction F. The direction of a bias magnetic fieldapplied to the first free magnetic layer 36 (the bias applicationdirection F) is perpendicular to the direction of a bias magnetic fieldapplied to the second free magnetic layer 46 (the bias applicationdirection F) when viewed along the Z1-Z2 axis.

Thus, the fixed magnetization direction P of the first pinned magneticlayer 34 is parallel to the fixed magnetization direction P of thesecond pinned magnetic layer 44. The bias application direction F of thefirst free magnetic layer 36 and the bias application direction F of thesecond free magnetic layer 46 tilt in the opposite directions relativeto the fixed magnetization direction P and are consequentlyperpendicular to each other when viewed along the Z1-Z2 axis.

Thus, when the application of an external magnetic field H to themagnetic sensor 101 along the X1-X2 axis rotates the magnetizationdirection of the first free magnetic layer 36 and the magnetizationdirection of the second free magnetic layer 46 in the direction of theexternal magnetic field H, these magnetization directions have differentrelationships with the fixed magnetization direction P (the Y1 directionon the Y1-Y2 axis). For example, for the external magnetic field H inthe X2 direction on the X1-X2 axis, both the magnetization direction ofthe first free magnetic layer 36 and the magnetization direction of thesecond free magnetic layer 46 rotate counterclockwise in FIG. 8. Therotation makes the magnetization direction of the first free magneticlayer 36 approximately perpendicular to the fixed magnetizationdirection P (the Y1 direction on the Y1-Y2 axis) and makes themagnetization direction of the second free magnetic layer 46 temporarilyparallel to and subsequently perpendicular to the fixed magnetizationdirection P (the Y1 direction on the Y1-Y2 axis). Thus, immediatelyafter the application of the external magnetic field H, the resistanceof the first magnetoresistive sensor M1 increases, but the resistance ofthe first magnetoresistive sensor M1 decreases. Thus, the differentialoutput (OutX1)−(OutX2) is negative. In contrast, for the externalmagnetic field H in the X1 direction on the X1-X2 axis, immediatelyafter the application of the external magnetic field H, the resistanceof the first magnetoresistive sensor M1 decreases, but the resistance ofthe first magnetoresistive sensor M1 increases. Thus, the differentialoutput (OutX1)−(OutX2) is positive.

Thus, immediately after the application of the external magnetic fieldH, the polarity of the differential output (OutX1)−(OutX2) depends onthe application direction of the external magnetic field H. Anadditional use of a feedback coil, for example, can therefore properlycontrol the direction of a coil current that generates a cancellationmagnetic field to cancel the external magnetic field H.

As described above, in the magnetic sensor 101, the exchange couplingmagnetic field Hex defines magnetization in the three directions: thefixed magnetization direction P in the first magnetoresistive sensor M1and the second magnetoresistive sensor M2 (the Y2 direction on the Y1-Y2axis), the bias application direction F in the first magnetoresistivesensor M1 (the X2-Y1 direction), and the bias application direction F inthe second magnetoresistive sensor M2 (X1-Y1 direction). To achievemagnetization in the three directions, like the magnetic sensor 100, themagnetic sensor 101 includes three materials with different blockingtemperatures as antiferromagnetic layers involved in the generation ofthe exchange coupling magnetic field Hex.

More specifically, each of the blocking temperature Tbf1 of the firstpinning antiferromagnetic layer 33 and the blocking temperature Tbf2 ofthe second pinning antiferromagnetic layer 43 is higher than theblocking temperature Tb1 of a first biasing antiferromagnetic layer 37and the blocking temperature Tb2 of a second biasing antiferromagneticlayer 47. The blocking temperature Tb1 of the first biasingantiferromagnetic layer 37 is higher than the blocking temperature Tb2of the second biasing antiferromagnetic layer 47. Thus, differentblocking temperatures can result in exchange coupling magnetic fields inthe three different directions.

As illustrated in FIG. 9A, the first magnetoresistive film MR1 formed ofthe tunneling magnetoresistive film includes a seed layer 32, the firstpinning antiferromagnetic layer 33, the first pinned magnetic layer 34,an insulating barrier layer 35, the first free magnetic layer 36, thefirst biasing antiferromagnetic layer 37, and an upper electrode 38 inthis order on a lower electrode 31 located on the substrate SB.

Table 3 shows a specific example of the first magnetoresistive film MR1.In Table 3, the leftmost column indicates each layer of the firstmagnetoresistive film MR1, and the second column from the rightindicates an example of the material of each layer. The numerical valuesin the rightmost column indicate the thickness of each layer (unit:angstrom (Å)).

TABLE 3 38 Upper electrode Ru 70 Ta 100 Ru 50 37 First biasingantiferromagnetic layer PtMn 300 36 First free Ferromagnetic layer90CoFe 10 magnetic layer Ferromagnetic layer 86NiFe 120 Ferromagneticlayer (50CoFe)B30 10 Ferromagnetic layer 50FeCo 10 35 Insulating barrierlayer MgO 20 34 First pinned Ferromagnetic layer 50FeCo 6 magnetic layerFerromagnetic layer (50CoFe)B30 10 Barrier layer Ta 3 Ferromagneticlayer 60FeCo 16 Nonmagnetic Ru 8 intermediate layer Ferromagnetic layer90CoFe 40 33 First pinning antiferromagnetic layer 20IrMn 8 50PtMn 1450PtCr 300 32 Seed layer NiFeCr 42 31 Lower electrode Ta 150 Cu 200 Ta30 Cu 200 Ta 30

The lower electrode 31 includes a 30-angstrom Ta layer, a 200-angstromCu layer, a 30-angstrom Ta layer, a 200-angstrom Cu layer, and a150-angstrom Ta layer on the substrate SB.

The seed layer 32 on the lower electrode 31 controls the crystallineorientation of layers formed thereon and is formed of Ru, Ni—Fe—Cr, orthe like. In Table 3, the seed layer 32 is a NiFeCr alloy layer 42angstroms in thickness.

The first pinning antiferromagnetic layer 33 is located on the seedlayer 32. A Pt_(50at%)Cr_(50at%) layer 300 angstroms in thickness, aPt_(50at%)Mn_(50at%) layer 14 angstroms in thickness, and anIr_(20at%)Mn_(80at%) layer 8 angstroms in thickness are layered on theseed layer 32 in this order to form the first pinning antiferromagneticlayer 33. The first pinning antiferromagnetic layer 33 is annealed forordering and forms, together with the first pinned magnetic layer 34,the first pinning exchange coupling film 532 by exchange coupling. Anexchange coupling magnetic field Hex is generated (at the interface)between the first pinning antiferromagnetic layer 33 and the firstpinned magnetic layer 34. The first pinning antiferromagnetic layer 33has a blocking temperature Tbf1 of approximately 500° C. Thus, theexchange coupling magnetic field Hex is maintained even when the firstpinning exchange coupling film 532 is heated to approximately 400° C.The layers to form the first pinning antiferromagnetic layer 33 areformed by sputtering or CVD, for example. In the formation of an alloylayer, such as the PtCr layer, metals for forming the alloy (Pt and Crfor the PtCr layer) may be simultaneously or alternately supplied. Forexample, metals for forming the alloy may be simultaneously sputtered,or different types of metal films may be alternately stacked.Simultaneous supply of metals for forming the alloy is sometimespreferred rather than alternate supply to increase the exchange couplingmagnetic field Hex.

As shown in Table 3, the first pinned magnetic layer 34 has a layeredferri structure composed of a ferromagnetic layer (90CoFe), anonmagnetic intermediate layer (Ru), and a ferromagnetic layer (50FeCo)located on the first pinning antiferromagnetic layer 33 in this order.The first pinned magnetic layer 34 also includes a barrier layer (Ta)and ferromagnetic layers ((50CoFe)B30 and 50FeCo). As described above,the first pinned magnetic layer 34 has fixed magnetization in onedirection (the Y1 direction on the Y1-Y2 axis in FIG. 9A) due to theexchange coupling magnetic field Hex between the first pinned magneticlayer 34 and the first pinning antiferromagnetic layer 33 and due to anRKKY interaction between the two ferromagnetic layers (90CoFe and60FeCo) on both sides of the nonmagnetic intermediate layer.

The insulating barrier layer 35 is located on the first pinned magneticlayer 34. In the embodiment in Table 3, the insulating barrier layer 35is a MgO layer 20 angstroms in thickness. The Mg content preferablyranges from 40 to 60 atomic percent. Mg_(50at%)O_(50at%) is morepreferred.

The first free magnetic layer 36 is located on the insulating barrierlayer 35. The first free magnetic layer 36 has a layered structurecomposed of a Co—Fe layer and a Co—Fe—B layer, for example. In theembodiment in Table 3, the first free magnetic layer 36 has a four-layerstructure (50FeCo, (50CoFe)B30, 86NiFe, 90CoFe). The magnetizationdirection of the first free magnetic layer 36 can be altered on the X-Yplane depending on the direction of the external magnetic field H. Toadjust the magnetization direction of the first free magnetic layer 36in the absence of the external magnetic field H, the first free magneticlayer 36 and the first biasing antiferromagnetic layer 37 form the firstbiasing exchange coupling film 531 by exchange coupling, and a biasmagnetic field associated with the exchange coupling magnetic field Hexin the first biasing exchange coupling film 531 is applied to the firstfree magnetic layer 36 in the X2-Y1 direction (in the bias applicationdirection F).

The first biasing antiferromagnetic layer 37 is located on the firstfree magnetic layer 36. In Table 3, the first biasing antiferromagneticlayer 37 is a Pt_(50at%)Mn_(50at%) layer 300 angstroms in thickness. Thefirst biasing antiferromagnetic layer 37 is annealed for ordering andforms, together with the first free magnetic layer 36, the first biasingexchange coupling film 531 by exchange coupling. An exchange couplingmagnetic field Hex is generated (at the interface) between the firstbiasing antiferromagnetic layer 37 and the first free magnetic layer 36.The first biasing antiferromagnetic layer 37 has a blocking temperatureTb1 of approximately 400° C. Thus, the exchange coupling magnetic fieldHex is maintained even when the first biasing exchange coupling film 531is heated to approximately 300° C.

The upper electrode 38 is located on the first biasing antiferromagneticlayer 37. In the embodiment in Table 3, the upper electrode 38 includesa Ru layer 50 angstroms in thickness, a Ta layer 100 angstroms inthickness, and a Ru layer 70 angstroms in thickness on the first biasingantiferromagnetic layer 37 in this order.

Table 4 shows a specific example of the second magnetoresistive filmMR2. In Table 4, the leftmost column indicates each layer of the secondmagnetoresistive film MR2, and the second column from the rightindicates an example of the material of each layer. The numerical valuesin the rightmost column indicate the thickness of each layer (unit:angstrom (Å)).

TABLE 4 48 Upper electrode Ru 70 Ta 100 Ru 50 47 Second biasingantiferromagnetic layer IrMn 80 46 Second free Ferromagnetic layer90CoFe 10 magnetic layer Ferromagnetic layer 86NiFe 120 Ferromagneticlayer (50CoFe)B30 10 Ferromagnetic layer 50FeCo 10 45 Insulating barrierlayer MgO 20 44 Second pinned Ferromagnetic layer 50FeCo 6 magneticlayer Ferromagnetic layer (50CoFe)B30 10 Barrier layer Ta 3Ferromagnetic layer 60FeCo 16 Nonmagnetic Ru 8 intermediate layerFerromagnetic layer 90CoFe 40 43 Second pinning antiferromagnetic layer20IrMn 8 50PtMn 14 50PtCr 300 42 Seed layer NiFeCr 42 41 Lower electrodeTa 150 Cu 200 Ta 30 Cu 200 Ta 30

A lower electrode 41, a seed layer 42, the second pinned magnetic layer44, an insulating barrier layer 45, the second free magnetic layer 46,and an upper electrode 48 have the same structure as the lower electrode31, the seed layer 32, the first pinned magnetic layer 34, theinsulating barrier layer 35, the first free magnetic layer 36, and theupper electrode 38, respectively, and are not described here.

A Pt_(50at%)Cr_(50at%) layer 300 angstroms in thickness, aPt_(50at%)Mn_(50at%) layer 14 angstroms in thickness, and anIr_(20at%)Mn_(80at%) layer 8 angstroms in thickness are layered on theseed layer 42 in this order to form the second pinning antiferromagneticlayer 43. The second pinning antiferromagnetic layer 43 is annealed forordering and forms, together with the second pinned magnetic layer 44,the second pinning exchange coupling film 542 by exchange coupling. Anexchange coupling magnetic field Hex is generated (at the interface)between the second pinning antiferromagnetic layer 43 and the secondpinned magnetic layer 44. The second pinning antiferromagnetic layer 43has a blocking temperature Tbf2 of approximately 500° C. Thus, theexchange coupling magnetic field Hex is maintained even when the secondpinning exchange coupling film 542 is heated to approximately 400° C.The layers to form the second pinning antiferromagnetic layer 43 areformed by sputtering or CVD, for example.

The second biasing antiferromagnetic layer 47 is an Ir_(20at%)Mn_(80at%)layer 80 angstroms in thickness. The second biasing antiferromagneticlayer 47 and the second free magnetic layer 46 form the second biasingexchange coupling film 541 and generate an exchange coupling magneticfield Hex (at the interface) between the second biasingantiferromagnetic layer 47 and the second free magnetic layer 46. Thesecond biasing antiferromagnetic layer 47 has a blocking temperature Tb2of approximately 300° C., which is lower than the blocking temperatureTb1 of the first biasing antiferromagnetic layer 37 (approximately 400°C.).

Thus, the magnetic sensor 101 includes the three antiferromagneticlayers with different blocking temperatures Tbs. In the magnetic sensor101 produced by forming and heating each layer as described below,therefore, each magnetoresistive sensor (the first magnetoresistivesensor M1, the second magnetoresistive sensor M2) can have a fixedmagnetization direction P and a bias application direction F inpredetermined directions.

First, the fixed magnetization axis setting step is performed. In thisstep, the first pinning antiferromagnetic layer 33 and the secondpinning antiferromagnetic layer 43 are ordered by heat treatment. Anyordering temperature may be used. The ordering temperature is typicallyslightly lower than the blocking temperature Tbf1 of the first pinningantiferromagnetic layer 33 and the blocking temperature Tbf2 of thesecond pinning antiferromagnetic layer 43, for example, approximately300° C. to 400° C. The heat-treatment time may also be any time,provided that the ordering can be achieved. For example, theheat-treatment time may be, but is limited to, one hour or more, morespecifically approximately five hours.

Thus, the first pinning antiferromagnetic layer 33 and the secondpinning antiferromagnetic layer 43 are ordered, and an exchange couplingmagnetic field Hex is generated in the first pinning exchange couplingfilm 532 and the second pinning exchange coupling film 542. In theordering, the magnetization direction of the first pinningantiferromagnetic layer 33 is adjusted to the magnetization direction ofthe first pinned magnetic layer 34. Thus, the exchange coupling magneticfield Hex in the first pinning exchange coupling film 532 is generatedin the magnetization direction of the first pinned magnetic layer 34. Inthe ordering, the magnetization direction of the second pinningantiferromagnetic layer 43 is adjusted to the magnetization direction ofthe second pinned magnetic layer 44. Thus, the exchange couplingmagnetic field Hex in the second pinning exchange coupling film 542occurs in the magnetization direction of the second pinned magneticlayer 44.

Thus, setting the magnetization directions of the first pinned magneticlayer 34 and the second pinned magnetic layer 44 in the Y1 direction onthe Y1-Y2 axis during the formation of the first pinned magnetic layer34 and the second pinned magnetic layer 44 can make the fixedmagnetization direction P of the first pinned magnetic layer 15 coaxialwith (more specifically, parallel to) the fixed magnetization directionP of the second pinned magnetic layer 25 in the fixed magnetization axissetting step. In the magnetic sensor 100 according to the firstembodiment, different film formation processes are required due toantiparallel magnetization directions of the first pinned magnetic layer15 and the second pinned magnetic layer 25. In the magnetic sensor 101according to the second embodiment, however, the first pinned magneticlayer 34 and the second pinned magnetic layer 44 can be formed by thesame film formation process.

If the magnetization direction of the first free magnetic layer 36 incontact with the first biasing antiferromagnetic layer 37 is preventedfrom being adjusted, the magnetization direction of the first biasingantiferromagnetic layer 37 is not adjusted in the fixed magnetizationaxis setting step. Likewise, if the magnetization direction of thesecond free magnetic layer 46 in contact with the second biasingantiferromagnetic layer 47 is prevented from being adjusted, themagnetization direction of the second biasing antiferromagnetic layer 47can be prevented from being adjusted in the fixed magnetization axissetting step.

Subsequently, in the first bias magnetic field setting step, heattreatment is performed at a temperature lower than the blockingtemperature Tbf1 of the first pinning antiferromagnetic layer 33 and theblocking temperature Tbf2 of the second pinning antiferromagnetic layer43 (for example, 350° C.). In the heat treatment, application of anexternal magnetic field in the X2-Y1 direction generates an exchangecoupling magnetic field Hex in the external magnetic field directionbetween the first biasing antiferromagnetic layer 37 and the first freemagnetic layer 36 and generates a bias magnetic field applied to thefirst free magnetic layer 36 in the X2-Y1 direction (in the biasapplication direction F). The bias application direction F of the firstfree magnetic layer 36 is nonparallel to the fixed magnetizationdirection P of the first pinned magnetic layer 34 and, morespecifically, is tilted 45 degrees in the X2 direction on the X1-X2 axiswhen viewed along the Z1-Z2 axis.

The heat-treatment temperature in the first bias magnetic field settingstep is lower than the blocking temperature Tbf1 of the first pinningantiferromagnetic layer 33 and the blocking temperature Tbf2 of thesecond pinning antiferromagnetic layer 43. Thus, the fixed magnetizationdirection P in the first pinned magnetic layer 34 and the fixedmagnetization direction P in the second pinned magnetic layer 44 are notchanged to the direction of the applied external magnetic field and aremaintained. Although an exchange coupling magnetic field Hex isgenerated between the second biasing antiferromagnetic layer 47 and thesecond free magnetic layer 46 in the first bias magnetic field settingstep, the direction of the exchange coupling magnetic field Hex betweenthe second biasing antiferromagnetic layer 47 and the second freemagnetic layer 46 can be chosen freely in a second bias magnetic fieldsetting step described below.

Finally, in the second bias magnetic field setting step, heat treatmentis performed at a temperature lower than the blocking temperature Tb1 ofthe first biasing antiferromagnetic layer 37 (for example, 300° C.). Inthe heat treatment, application of an external magnetic field in theX1-Y1 direction generates an exchange coupling magnetic field Hex in theexternal magnetic field direction between the second biasingantiferromagnetic layer 47 and the second free magnetic layer 46, and abias magnetic field is applied to the second free magnetic layer 46 inthe X1-Y1 direction (in the bias application direction F). The biasapplication direction F of the second free magnetic layer 46 isnonparallel to the fixed magnetization direction P of the second pinnedmagnetic layer 44 and, more specifically, is tilted 45 degrees in the X1direction on the X1-X2 axis when viewed along the Z1-Z2 axis.

The heat-treatment temperature in the second bias magnetic field settingstep is lower than the blocking temperature Tbf1 of the first pinningantiferromagnetic layer 33, the blocking temperature Tbf2 of the secondpinning antiferromagnetic layer 43, and the blocking temperature Tb1 ofthe first biasing antiferromagnetic layer 37. Thus, the fixedmagnetization direction P in the first pinned magnetic layer 34, thefixed magnetization direction P in the second pinned magnetic layer 44,and the direction of a bias magnetic field applied to the first freemagnetic layer 36 (the bias application direction F) are not changed tothe direction of the magnetic field applied and are maintained.

Thus, when the magnetic sensor 101 includes the three antiferromagneticlayers with different blocking temperatures Tbs, the above step cangenerate an exchange coupling magnetic field Hex in any direction in theferromagnetic layers exchange-coupled with the antiferromagnetic layers(the first pinned magnetic layer 34, the second pinned magnetic layer44, the first free magnetic layer 36, and the second free magnetic layer46).

These embodiments are described to facilitate the understanding of thepresent invention and do not limit the present invention. Thus, thecomponents disclosed in the embodiments encompass all design changes andequivalents thereof that fall within the technical scope of the presentinvention.

For example, in the magnetic sensor 100 according to the firstembodiment, the fixed magnetization direction P is perpendicular to thebias application direction F in each of the first magnetoresistivesensor M1 and the second magnetoresistive sensor M2, the fixedmagnetization direction P in the first magnetoresistive sensor M1 isantiparallel to the fixed magnetization direction P in the secondmagnetoresistive sensor M2, and the bias application direction F in thefirst magnetoresistive sensor M1 is parallel to the bias applicationdirection F in the second magnetoresistive sensor M2. As in the magneticsensor 101 according to the second embodiment, however, the fixedmagnetization direction P in the first magnetoresistive sensor M1 may beparallel to the fixed magnetization direction P in the secondmagnetoresistive sensor M2, and the bias application direction F in thefirst magnetoresistive sensor M1 and the bias application direction F inthe second magnetoresistive sensor M2 may be tilted in the oppositedirections relative to the fixed magnetization direction P and may beperpendicular to each other. The relationship between the fixedmagnetization direction P and the bias application direction F of themagnetic sensor 101 according to the second embodiment may be the sameas in the magnetic sensor 100 according to the first embodiment.

Although the first magnetoresistive film MR1 and the secondmagnetoresistive film MR2 in the magnetic sensor 100 according to thefirst embodiment are giant magnetoresistive films, they may be tunnelingmagnetoresistive films as in the second embodiment. Although the firstmagnetoresistive film MR1 and the second magnetoresistive film MR2 inthe magnetic sensor 101 according to the second embodiment are tunnelingmagnetoresistive films, they may be giant magnetoresistive films as inthe first embodiment.

Although the first magnetoresistive film MR1 and the secondmagnetoresistive film MR2 in the magnetic sensor 100 according to thefirst embodiment have a top-pinned structure, which includes a freemagnetic layer near the substrate SB, they may have a bottom-pinnedstructure, which has a pinned magnetic layer near the substrate SB, asin the second embodiment. Although the first magnetoresistive film MR1and the second magnetoresistive film MR2 in the magnetic sensor 101according to the second embodiment have the bottom-pinned structure,which includes a pinned magnetic layer near the substrate SB, they mayhave the top-pinned structure, which has a free magnetic layer near thesubstrate SB, as in the first embodiment.

Although the free magnetic layer and the pinned magnetic layer in themagnetic sensor 100 according to the first embodiment and the magneticsensor 101 according to the second embodiment have a multilayerstructure, one or both of the free magnetic layer and the pinnedmagnetic layer may have a monolayer structure.

EXAMPLES

Although the present invention is more specifically described in thefollowing examples, the scope of the present invention is not limited tothese examples.

Example 1

A multilayer film with the following structure was formed to examine therelationship between the intensity of an exchange coupling magneticfield Hex and the ambient temperature. Each numerical value inparentheses indicates the thickness of the corresponding layer (unit:angstroms).

Substrate/underlayer: NiFeCr (42)/antiferromagnetic layer/pinnedmagnetic layer: 90CoFe (100)/protective layer: Ta (90)

In the present example, the antiferromagnetic layer had a multilayerstructure of 54PtCr (280)/50PtMn (20) located on the underlayer in thisorder. The multilayer film was annealed in a 1-kOe magnetic field at400° C. for 5 hours, and the magnetization of each of the pinnedmagnetic layer and the antiferromagnetic layer was fixed to form anexchange coupling film.

Example 2

The multilayer structure of the antiferromagnetic layer in Example 1 waschanged to 50PtMn (300). The multilayer film was annealed in a 1-kOemagnetic field at 300° C. for 4 hours, and the magnetization of each ofthe pinned magnetic layer and the antiferromagnetic layer was fixed toform an exchange coupling film.

Example 3

The multilayer structure of the antiferromagnetic layer in Example 1 waschanged to 20IrMn (80). The multilayer film was annealed in a 1-kOemagnetic field at 300° C. for 1 hour, and the magnetization of each ofthe pinned magnetic layer and the antiferromagnetic layer was fixed toform an exchange coupling film.

Magnetization curves of the exchange coupling films according toExamples 1 to 3 were obtained with a vibrating sample magnetometer (VSM)at different ambient temperatures (unit: ° C.). The exchange couplingmagnetic field Hex (unit: Oe) was determined at each temperature fromthe resulting hysteresis loop. Tables 5 to 7 list the exchange couplingmagnetic field Hex at each temperature and the exchange couplingmagnetic field Hex at each temperature normalized with respect to theexchange coupling magnetic field Hex at room temperature (aroom-temperature-normalized exchange coupling magnetic field). FIG. 10is a graph of the relationship between the room-temperature-normalizedexchange coupling magnetic field and the measurement temperature.

TABLE 5 Example 1 Temperature Hex Normalized (° C.) (Oe) Hex 22 530 1.0042 540 1.02 63 525 0.99 84 540 1.02 104 525 0.99 125 510 0.96 144 5100.96 165 500 0.94 184 480 0.91 204 480 0.91 224 475 0.90 268 465 0.88305 425 0.80 345 395 0.75 385 365 0.69 424 275 0.52 463 165 0.31 500 500.09

TABLE 6 Example 2 Temperature Hex Normalized ° C.) (Oe) Hex 22 278 0.9943 278 0.99 65 270 0.97 85 267 0.96 101 260 0.93 125 250 0.90 145 2430.87 167 240 0.86 182 224 0.80 201 216 0.77 222 210 0.75 254 185 0.66304 123 0.44 345 55 0.20 365 26 0.09 397 0 0.00

TABLE 7 Example 3 Temperature Hex Normalized (° C.) (Oe) Hex 23 95 1.0040 91 0.96 62 85 0.89 84 80 0.84 102 74 0.78 123 67 0.71 145 56 0.59 16649 0.52 183 43 0.45 203 34 0.36 234 25 0.26 260 13 0.14 294 0 0.00

Tables 5 to 7 and FIG. 10 show that the exchange coupling filmsaccording to Examples 1 to 3 differently maintain the exchange couplingmagnetic field Hex at each ambient temperature. In particular, theexchange coupling film with the multilayer antiferromagnetic layeraccording to Example 1 can maintain the exchange coupling magnetic fieldHex even at a temperature in the range of 350° C. to 400° C., at whichthe exchange coupling films according to Examples 2 and 3 substantiallylose the exchange coupling magnetic field Hex.

What is claimed is:
 1. A magnetic detector comprising a full-bridgecircuit including a first magnetoresistive sensor and a secondmagnetoresistive sensor, the first magnetoresistive sensor including afirst magnetoresistive film including a first pinned magnetic layer anda first free magnetic layer, the second magnetoresistive sensorincluding a second magnetoresistive film including a second pinnedmagnetic layer and a second free magnetic layer, wherein: thefull-bridge circuit includes a first half-bridge circuit and a secondhalf-bridge circuit connected in parallel between a power supplyterminal and a ground terminal, the first half-bridge circuit includingthe first magnetoresistive sensor and the second magnetoresistive sensorconnected in series, the second half-bridge circuit including the secondmagnetoresistive sensor and the first magnetoresistive sensor connectedin series, the first magnetoresistive sensor and the secondmagnetoresistive sensor are located on a same substrate, in the firstmagnetoresistive film, the first pinned magnetic layer and a firstpinning antiferromagnetic layer located on an opposite side of the firstpinned magnetic layer from the first free magnetic layer constitute afirst pinning exchange coupling film, and the first free magnetic layerand a first biasing antiferromagnetic layer located on an opposite sideof the first free magnetic layer from the first pinned magnetic layerconstitute a first biasing exchange coupling film, in the secondmagnetoresistive film, the second pinned magnetic layer and a secondpinning antiferromagnetic layer located on an opposite side of thesecond pinned magnetic layer from the second free magnetic layerconstitute a second pinning exchange coupling film, and the second freemagnetic layer and a second biasing antiferromagnetic layer located onan opposite side of the second free magnetic layer from the secondpinned magnetic layer constitute a second biasing exchange couplingfilm, the first pinned magnetic layer has a fixed magnetization axiscoaxial with a fixed magnetization axis of the second pinned magneticlayer, the first biasing exchange coupling film has an exchange couplingmagnetic field direction nonparallel to a fixed magnetization axisdirection of the first pinned magnetic layer, and the second biasingexchange coupling film has an exchange coupling magnetic field directionnonparallel to a fixed magnetization axis direction of the second pinnedmagnetic layer, each of a blocking temperature (Tbf1) of the firstpinning antiferromagnetic layer and a blocking temperature (Tbf2) of thesecond pinning antiferromagnetic layer is higher than a blockingtemperature (Tb1) of the first biasing antiferromagnetic layer and ablocking temperature (Tb2) of the second biasing antiferromagneticlayer, and the blocking temperature (Tb1) of the first biasingantiferromagnetic layer is higher than the blocking temperature (Tb2) ofthe second biasing antiferromagnetic layer.
 2. The magnetic detectoraccording to claim 1, wherein: the fixed magnetization axis direction ofthe first pinned magnetic layer is antiparallel to the fixedmagnetization axis direction of the second pinned magnetic layer, thefirst biasing antiferromagnetic layer has an exchange coupling magneticfield direction parallel to an exchange coupling magnetic fielddirection of the second biasing antiferromagnetic layer, and the fixedmagnetization axis direction of the first pinned magnetic layer isnonparallel to the exchange coupling magnetic field direction of thefirst biasing antiferromagnetic layer.
 3. The magnetic detectoraccording to claim 1, wherein: the fixed magnetization axis direction ofthe first pinned magnetic layer is parallel to the fixed magnetizationaxis direction of the second pinned magnetic layer, and the firstbiasing exchange coupling film has a bias magnetic field directionnonparallel to a bias magnetic field direction of the second biasingexchange coupling film.
 4. The magnetic detector according to claim 3,wherein a tilt angle of the bias magnetic field direction of the firstbiasing exchange coupling film relative to the fixed magnetization axisdirection of the first pinned magnetic layer viewed in a stackingdirection is oppositely-directed to and has the same absolute value as atilt angle of the bias magnetic field direction of the second biasingexchange coupling film relative to the fixed magnetization axisdirection of the second pinned magnetic layer viewed in the stackingdirection.
 5. The magnetic detector according to claim 4, wherein thefirst biasing antiferromagnetic layer is a PtMn layer, and the secondbiasing antiferromagnetic layer is an IrMn layer.
 6. The magneticdetector according to claim 1, wherein: at least one of the firstpinning antiferromagnetic layer and the second pinning antiferromagneticlayer includes an X(Cr—Mn) layer containing one or two or more elementsX selected from the group consisting of platinum group elements and Niand containing Mn and Cr, the X(Cr—Mn) layer has a first region locatedrelatively near a pinning ferromagnetic layer exchange-coupled with thepinning antiferromagnetic layer and a second region located relativelyfar from the pinning ferromagnetic layer, and the first region has ahigher Mn content than the second region.
 7. The magnetic detectoraccording to claim 6, wherein the first region is in contact with thepinning ferromagnetic layer.
 8. The magnetic detector according to claim6, wherein the first region has a portion with a Mn/Cr ratio of 0.3 ormore, the Mn/Cr ratio being a ratio of the Mn content to a Cr content.9. The magnetic detector according to claim 8, wherein the first regionhas a portion with a Mn/Cr ratio of 1 or more.
 10. The magnetic detectoraccording to claim 6, wherein the pinning antiferromagnetic layerincludes a PtCr layer and an X⁰Mn layer located nearer the pinningferromagnetic layer than the PtCr layer, wherein X⁰ denotes one or twoor more elements selected from the group consisting of platinum groupelements and Ni.
 11. The magnetic detector according to claim 6, whereinthe pinning antiferromagnetic layer includes a PtCr layer and a PtMnlayer, the PtMn layer being located nearer the pinning ferromagneticlayer.
 12. The magnetic detector according to claim 11, furthercomprising an IrMn layer located nearer the pinning ferromagnetic layerthan the PtMn layer.
 13. The magnetic detector according to claim 1,wherein at least one of the first pinning antiferromagnetic layer andthe second pinning antiferromagnetic layer has an alternately layeredstructure of alternately stacked three or more layers composed of anX¹Cr layer wherein X¹ denotes one or two or more elements selected fromthe group consisting of platinum group elements and Ni and an X²Mn layerwherein X² denotes one or two or more elements selected from the groupconsisting of platinum group elements and Ni and may be the same as ordifferent from X¹.
 14. The magnetic detector according to claim 13,wherein X¹ is Pt, and X² is Pt or Ir.
 15. The magnetic detectoraccording to claim 13, wherein the pinning antiferromagnetic layerincludes a unit layered portion including a stack of units composed ofthe X¹Cr layer and the X²Mn layer.
 16. The magnetic detector accordingto claim 15, wherein in the unit layered portion, the X¹Cr layers havethe same thickness, and the X²Mn layers have the same thickness, theX¹Cr layers having a larger thickness than the X²Mn layers.
 17. Themagnetic detector according to claim 16, wherein a ratio of thethickness of the X¹Cr layer to the thickness of the X²Mn layer rangesfrom 5:1 to 100:1.
 18. A method for producing a magnetic detectorincluding a full-bridge circuit including a first magnetoresistivesensor and a second magnetoresistive sensor, the first magnetoresistivesensor including a first magnetoresistive film including a first pinnedmagnetic layer and a first free magnetic layer, the secondmagnetoresistive sensor including a second magnetoresistive filmincluding a second pinned magnetic layer and a second free magneticlayer, wherein: the full-bridge circuit includes a first half-bridgecircuit and a second half-bridge circuit connected in parallel between apower supply terminal and a ground terminal, the first half-bridgecircuit including the first magnetoresistive sensor and the secondmagnetoresistive sensor connected in series, the second half-bridgecircuit including the second magnetoresistive sensor and the firstmagnetoresistive sensor connected in series, the first magnetoresistivesensor and the second magnetoresistive sensor are located on a samesubstrate, in the first magnetoresistive film, the first pinned magneticlayer and a first pinning antiferromagnetic layer located on an oppositeside of the first pinned magnetic layer from the first free magneticlayer constitute a first pinning exchange coupling film, and the firstfree magnetic layer and a first biasing antiferromagnetic layer locatedon an opposite side of the first free magnetic layer from the firstpinned magnetic layer constitute a first biasing exchange coupling film,in the second magnetoresistive film, the second pinned magnetic layerand a second pinning antiferromagnetic layer located on an opposite sideof the second pinned magnetic layer from the second free magnetic layerconstitute a second pinning exchange coupling film, and the second freemagnetic layer and a second biasing antiferromagnetic layer located onan opposite side of the second free magnetic layer from the secondpinned magnetic layer constitute a second biasing exchange couplingfilm, each of a blocking temperature (Tbf1) of the first pinningantiferromagnetic layer and a blocking temperature (Tbf2) of the secondpinning antiferromagnetic layer is higher than a blocking temperature(Tb1) of the first biasing antiferromagnetic layer and a blockingtemperature (Tb2) of the second biasing antiferromagnetic layer, and theblocking temperature (Tb1) of the first biasing antiferromagnetic layeris higher than the blocking temperature (Tb2) of the second biasingantiferromagnetic layer, the method comprising: setting a fixedmagnetization axis by ordering the first pinning antiferromagnetic layerand the second pinning antiferromagnetic layer by heat treatment togenerate an exchange coupling magnetic field in the first biasingexchange coupling film and in the second biasing exchange coupling film,thereby making a fixed magnetization axis of the first pinned magneticlayer coaxial with a fixed magnetization axis of the second pinnedmagnetic layer, setting a first bias magnetic field by making adirection of a bias magnetic field generated by the first biasingexchange coupling film nonparallel to a fixed magnetization axisdirection of the first pinned magnetic layer by heat treatment in anexternal magnetic field at a temperature lower than a blockingtemperature (Tbf1) of the first pinning antiferromagnetic layer and ablocking temperature (Tbf2) of the second pinning antiferromagneticlayer, and after setting the first bias magnetic field, setting a secondbias magnetic field by making a direction of a bias magnetic fieldgenerated by the second biasing exchange coupling film nonparallel to afixed magnetization axis direction of the second pinned magnetic layerby heat treatment in an external magnetic field at a temperature lowerthan the blocking temperature (Tb1) of the first biasingantiferromagnetic layer.
 19. The method for producing a magneticdetector according to claim 18, wherein setting the fixed magnetizationaxis includes adjusting an exchange coupling magnetic field direction ofthe first pinning exchange coupling film to a magnetization direction ofthe first pinned magnetic layer and adjusting an exchange couplingmagnetic field direction of the second pinning exchange coupling film toa magnetization direction of the second pinned magnetic layer.
 20. Themethod for producing a magnetic detector according to claim 18, wherein:setting the fixed magnetization axis includes making the fixedmagnetization axis direction of the first pinned magnetic layerantiparallel to the fixed magnetization axis direction of the secondpinned magnetic layer, setting the first bias magnetic field includesmaking the exchange coupling magnetic field direction of the firstbiasing antiferromagnetic layer nonparallel to the fixed magnetizationaxis direction of the first pinned magnetic layer, and setting thesecond bias magnetic field includes making an exchange coupling magneticfield direction of the second biasing antiferromagnetic layer parallelto the exchange coupling magnetic field direction of the first biasingantiferromagnetic layer.
 21. The method for producing a magneticdetector according to claim 18, wherein: setting the fixed magnetizationaxis includes making the fixed magnetization axis direction of the firstpinned magnetic layer parallel to the fixed magnetization axis directionof the second pinned magnetic layer, setting the first bias magneticfield includes making a bias magnetic field direction of the firstbiasing exchange coupling film nonparallel to the fixed magnetizationaxis direction of the first pinned magnetic layer, and setting thesecond bias magnetic field includes making a bias magnetic fielddirection of the second biasing exchange coupling film nonparallel toboth the fixed magnetization axis direction of the first pinned magneticlayer and the bias magnetic field direction of the first biasingexchange coupling film.